We study the relative dust attenuation–inclination relation in 78,721 nearby galaxies using the axis ratio dependence of optical–NIR colour , as measured by the Sloan Digital Sky Survey ( SDSS ) , the Two Micron All Sky Survey ( 2MASS ) , and the Wide-field Infrared Survey Explorer ( WISE ) .
In order to avoid to the greatest extent possible attenuation-driven biases , we carefully select galaxies using dust attenuation-independent near- and mid-IR luminosities and colours .
Relative u -band attenuation between face-on and edge-on disc galaxies along the star forming main sequence varies from \sim 0.55 mag up to \sim 1.55 mag .
The strength of the relative attenuation varies strongly with both specific star formation rate and galaxy luminosity ( or stellar mass ) .
The dependence of relative attenuation on luminosity is not monotonic , but rather peaks at M _ { 3.4 \umu \text { m } } \approx - 21.5 , corresponding to M _ { * } \approx 3 \times 10 ^ { 10 } M _ { \sun } .
This behavior stands seemingly in contrast to some older studies ; we show that older works failed to reliably probe to higher luminosities , and were insensitive to the decrease in attenuation with increasing luminosity for the brightest star-forming discs .
Back-of-the-envelope scaling relations predict the strong variation of dust optical depth with specific star formation rate and stellar mass .
More in-depth comparisons using the scaling relations to model the relative attenuation require the inclusion of star-dust geometry to reproduce the details of these variations ( especially at high luminosities ) , highlighting the importance of these geometrical effects .